Body composition, including muscle, is influenced both by genetic factors and environmental stimuli. Genetic factors are typically difficult, if not impossible to alter through intervention. Environmental factors however are routinely manipulated and important environmental factors that effect muscle metabolism, such as food intake and exercise, effect muscle metabolism within hours of stimulation A Gene and protein expression patterns change in response to these stimuli. These changes result in muscle adaptations such as muscle atrophy (loss) via muscle protein catabolism (breakdown) or muscle hypertrophy (increase) via muscle protein accretion. These opposing actions are not mutually exclusive and the determination of muscle loss or gain is the net effect of both positive and negative factors governing muscle development.
Exercise is a major stimulus of skeletal muscle growth. During several hours post-exercise there are dynamic changes in the rates of both skeletal muscle synthesis and breakdown. The consumption of specific dietary components is known to further influence the response of skeletal muscle to exercise. The main component of food that is known to stimulate increased muscle protein synthesis is amino acids (Rennie M J. Body maintenance and repair: how food and exercise keep the musculoskeletal system in good shape. Exp Physiol. 2005 July; 90(4):427-36). Increased levels of circulating essential amino acids have been shown to stimulate protein synthesis (Smith K, Reynolds N, Downie S, Patel A, Rennie M J. Effects of flooding amino acids on incorporation of labeled amino acids into human muscle protein. Am J Physiol. 1998 July; 275(1 Pt 1):E73-8).
Exercise stimulates inflammatory pathways which contribute to anabolic responses. However, excessive activation of inflammatory signaling molecules such as Nuclear Factor kappa B (NE-κB) has been implicated in several disease states involving loss or weakening of muscle (Kramer H F, Goodyear L J. Exercise, MAPK, and NF-{kappa}B Signaling in Skeletal Muscle. J Appl Physiol. 2007 Feb. 15). In these situations skeletal muscle protein breakdown exceeds protein synthesis.
It would therefore be advantageous for an individual concerned with maintaining or increasing lean skeletal muscle mass to consume a nutritional composition directed at improving skeletal muscle metabolism, to encourage skeletal muscle protein synthesis while minimizing skeletal muscle protein breakdown.